Gas detectors are used to detect the presence, and measure the concentration of, gases or other volatile compounds. Among other uses, they may be employed in a monitoring system to, for instance, detect the presence of                (i) a toxic gas (eg (a) ammonia released in an enclosed space, (b) carbon dioxide or carbon monoxide produced from a controlled fire event such as fuel fired furnaces, gas hot water heaters, gas stoves, gas dryers, space heaters, charcoal grills, fireplaces, vehicles (including build-up in carparks), and lawn movers, and (c) methyl isocyanate gas accidentally released from an industrial manufacturing plant);        (ii) a flammable gas leak (in an effort to prevent fire), or flammable gas build-up (eg methane in sewage systems); and/or        (iii) a gas or other volatile compound that is indicative of an impending fire (ie smouldering or melting materials) or pre-existing fire (ie burning materials) or the nature of a fire (e.g. the type of material that is burning).        
Although in this specification the gas detector will be predominantly described in relation to the latter (ie the prevention and detection of an undesirable fire event) for ease of understanding, this should not limit the scope of the invention. Clearly, a gas detector is also useful in other situations.
It is an object of the present invention to provide an improved gas detector apparatus. In some aspects, the present invention seeks to provide an improved gas detector apparatus that incorporates or can be used in conjunction with a smoke detector. In some aspects, the present invention seeks to provide an improved gas detector apparatus that can be used in conjunction with air sampling pollution monitoring equipment such as an aspirated smoke detector with an associated sampling pipe network.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.